Production of pulp



Patented Nov. 15, 1932 UNITED STATES PATENT OFFICE LINN BRADLEY, OF MONTCLAIR, NEW JERSEY, AND EDWARD P. MCKEEFE, OI PLATTE- BURG, NEW YORK, ASSIGNORS TO BRADLEY-MCKEEFE CORPORATION, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK PRODUCTION OF PULP No Drawing. Original application filed March 28, 1921, Serial No. 456,187. Divided and this application filed March 2, 1925.

This invention relates to improvements in processes of cooking wood chips for the production of wood cellulose products or pulp therefrom.

The present invention includes improvements in the carrying out of the cooking operation for the cooking of wood with the acid sulfite process, when carried out with a sulfite cooking liquor containing a sulfite of an alkali, as well as improvements in a modified soda pulp process in which the cooking liquor contains caustic alkali and sodium sulfite.

The present invention includes an 1mproved method of carrying out a sulfite process (including both the acid sulfite process making use of sodium acid sulfite or .bisulfite and the alkaline sulfite process, making use of caustic soda and sodium sulfite), according to which the digester is subjected to exhaustion, after it is filled with chips and before adding the cooking liquor, in order to exhaust air or other gases or vapors therefrom. This exhaustion is facilitated by heat which may come from the residual heat left in the digester from the previous cook. One preferred method of exhausting air, gases, etc., is by means of a vacuum tank of sufiicient capacity to insure the reduction of pressure within the digester to the desired point with in a comparatively short time. For instance, the digester may be filled with chips, closed, and the cover sealed, and all other openings closed except the opening in the pipe connecting the vacuum tank with the particular digester to be exhausted. By operating a vacuum pump in connection with the vacuum tank. and continuing the operation of the pump during the exhaustion operation, the pressure can be reduced to the desired degree. and the greater part of the air, gases, etc, thus removed from the digester and the chips therein within a relatively short time. One vacuum tank may thus serve for a battery of digesters, and. after a particular diges.er has been exhausted as described, a reserve vacuum may be built up in the vacuum tank, for use with other digesters, as each in turn has been filled with chips.

By subjecting the chips to a vacuum in this Serial N0. 12,760.

way, the chips are freed from air, gases, etc., to such a degree that they are much more readily and thoroughly penetrable by the cooking liquor or by gaseous sulfur dioxide. After the chips have been thus exhausted, we then supply the cooking liquor, which may be any of the cooking liquors hereinbefore described; and such cooking liquor will act in a more uniform and advantageous manner than when introduced into digesters containing chips having their pores air-bound or fille with other gases or vapors.

Instead of adding the cooking liquor directly to the digester after the evacuation, a particularly advantageous method of procedure is to introduce gaseous sulfur dioxide to fill the available space in the digester and to thoroughly penetrate the wood chips or other material. Thus, after the vacuum has been reduced to the desired degree and maintained for a suitable time, the connection between the digester and the vacuum tank may be closed, and the digester then connected with a source of sulfur dioxide, such as a storage tank of liquor capable of giving up sulfur dioxide when heated or subjected to reduced pressure or both, or a source of liquid sulfur dioxide which will be vaporized, and the vapors supplied to the digester. The sulfur dioxide thus supplied will thoroughly penetrate the wood chips or other material.

After the digester has thus been evacuated and filled with sulfur dioxide, cooking liquor of the desired composition and temperature is introduced in such manner as to ermit the sulfur dioxide contained in the digester to be absorbed by the cooking liquor. The cooking liquor may thus be introduced under pressure to promote the absorption of sulfur dioxide thereby. The liquor will thus come in contact with chips already impregnated with sulfur dioxide, and the liquor will be strengthened by the sulfur dioxide thus contained, as the liquor penetrates the chips and absorbs the sulfur dioxide contained therein. This enables a stronger sulfite cooking liquor to be produced in place in the digester, and increases the local concentration of the liquor in sulfur dioxide (free or combined) which penetrates the wood chips. The chips are thus cooked more uniformly and more rapidly, and with less loss of fibre than if the process were carried out 1n the usual way.

The cooking liquor which may besupplied to the digester, filled with sulfur dioxide as above described, ay be either an acld sulfite liquor, the sulfur dioxide content of which will be increased by that contained in the digester; or it may be an alkaline liquor which will combine with the sulfur dioxide to form a corresponding amount of alkali sulfite. Thatis, the im rovement in the sulfite process above descri ed is applicable both to the acid sulfite process and to the alkaline sulfite process, hereinbefore described.

Furthermore, the exhaustion and removal of air and other gases or vapors from the chips to be cooked is an advantageous treatment in connection with other processes than the sulfite processes, such as the soda pulp process, etc.

The introduction of sulfur dioxide prior to the introduction of the cooking liquor also makes possible the combination of an acid cook with a subsequent alkaline cook. The liquor first introduced may be of an acid reaction, and the first part of the cooking operation may be carried out with an acid sulfite liquor, and, thereafter, a suificient amount of alkali or alkali compound may be introduced to neutralize all of the free sulfurous acid together with an additional amount of alkali so as to produce an alkaline cooking liquor of the desired composition, so that the cook will be finished with an alkaline sulfite cooking liquor.

The bisulfite process of the present invention makes use of a sulfite liquor containing uncombined sulfurous acid together with sodium sulfite or a bisulfite, instead of calcium bisulfite. The digestion of the wood chips with the sulfite liquor may thus be carried out with a liquor containing twenty grams of sodium bisulfite per liter, and the digestion can be carried out in much the usual way by heating with direct steam at a pressure around fifty to eighty pounds and for a suitable period of time, for example, from 3 to 10 hours. Upon completion of the cook in the sulfite process, when carried out with sulfurous acid and sodium sulfite or bisulfite, free sulfur dioxide is blown or relieved from the digester at the end of the cook and the pulp is separated from the residual sulfite liquor.

The alkali sulfite process of the present invention makes use of a cooking liquor which is an alkaline liquor containing a sulfite of an alkali. This method is distinguished from the acid sulfite process, above described, by the fact that an excess of free sulfurous acid or sodium bisulfite is absent, and by the fact that caustic soda is present in sufficient amount to give an alkaline cooking liquor of appropriate strength, while sodium sulfite is also present in substantial amount. This cooking method is distinguished from the soda process by the resence in the cooking liquor of a regulated amount of sodium sulfite, in addition to the caustic soda; and it is distinguished from the sulfate process, socalled, by the absence of large amounts of sodium sulfide and the presence of sodium sulfite. 'The composite cooking liquor, containing caustic soda and sodium sulfite, can vary somewhat in its com osition and in the proportions of caustic so a and sodium sulfite. Ordinarily a preponderating proportion of caustic soda will be used, for example. so that from to of the total sodium of the cooking liquor will be present as caustic soda and the remainder mainly as sodium sulfite. A cooking liquor may thus be used containing at least 40 grams of sodium per liter, of which at least 40% is present as sodium hydroxide and at least 5% as sodium sulfite, with the particular amounts of caustic soda and sodium sulfite, varying somewhat above these percentages. By the use of such an alkaline cooking liquor containing sulfites, it is possible to produce satisfactory pulp or cellulose material from forest products and other cellulose-bearing materials which, due to their inherent composition and properties, have been unsuited to the production of high as grade cellulose material by the processes heretofore commonly practiced. Materials such as woods and other forest material of inferior value (for treatment according to common methods) as well as materials such as bagasse, reeds, grasses, bamboo, corn stalks, straw, etc., can advantageously be subjected to digestion with such alkaline sulfite cooking liquor and high grade pulp or cellulose material produced therefrom. This method, therefore, increases the available supply of raw materials for the production of high grade pulp or cellulose products.

In carrying out the digestion with such an alkaline sulfite liquor, the time of treatment and the temperature, pressure, etc., can be varied, depending upon the particular wood or other material undergoing digestion; but the process can be carried out under similar conditions of temperature and pressure to those commonly used in the soda or sulfate process. The digestion will, however, be modified by the action of the composite cooking liquor so that less injury to the cellulose material will take place and so that a superior pulp or cellulose material will be produced.

The acid sulfite process, and thealkali sulfite process, of the present invention can advantageously be combined into cyclic processes in which the residual liquors from one process are used in making the cooking liquors for the other process, as more fully described in our parent application Serial No. 456,187 filed March 28, 1921 of whichthe present application is a division.

According to another embodiment of the present invention, a part or all of the sodium sulfite may be replaced by thiosulfate. For example, the alkaline sulfite liquor may be composed of caustic soda and sodium thio sulfate, instead of caustic soda and sodium sulfite, or it may be composed of all three ingredients, namely, caustic soda, sodium sulfite and sodium thiosulfate. The liquor may also contain other compounds than those mentioned, such for example as sodium sulfate sodium carbonate or sodium sulfide.

Our investigations have shown that if some untreated black liquor is mixed with new cooking liquor containing caustic soda, a portion of the caustic soda is used up in the formation of other sodium compounds by reaction either directly or indirectly between the caustic soda and soluble organic compounds so that the total content of caustic soda is not available for cooking the wood chips in the same way that it would be if no such soluble organic constituents were present. Sodium sulfite and sodium thio-sulfate exert a retarding influence upon the reaction between the caustic soda and the soluble organic compounds and likewise upon the cellu lose so that the caustic soda can act more of fectively and so that the destructive action for the same total amount of caustic soda is minimized.

\Ve claim:

1. The improvement in the cooking of wood with a cooking liquor containing caustic alkali and a sulfite of an alkali which comprises subjecting the wood chips to a vacuum, introducing gaseous sulfur dioxide into the evacuated chips, and supplying an alkaline cooking liquor to combine with the sulfur dioxide.

2. The improvement in the cooking of wood for the production of wood pulp therefrom, which comprises subjecting wood chips in a digester to the action of sulfur dioxide, and subsequently introducing an alkaline cooking liquor sufiicient in amount to combine with all of the sulfur dioxide and to give an excess of alkali in the cooking liquor. 7 The improvement in the cooking of wood for the production of wood pulp therefrom, which comprises subjecting the wood chips in a digester to a vacuum, introducing sulfur dioxide into the evacuated digester, then introducing a cooking liquor and sub jecting the wood toapartialcookingoperation with an acid sulfite liquor, thereafter introducing a sufficient amount of alkali or alkali compounds to neutralize all of the free sulfurous acid together an additional amount of alkali to produce an alkaline cooking liquor, and subjecting the partially cooked wood to a further cooking operation with such alkaline sulfite cooking liquor.

l. The improvement in the sulfite process which comprises subjecting the charge in the digester to a preliminary digestion with an acid sulfite liquor, subsequently introducing sufiicient caustic soda to give an alkaline sulfite liquor and completing the digestion with such liquor.

5. The improvement in the cooking of wood for the production of wood pulp therefrom which comprises subjecting wood chips in a digester to the action of sulfurous acid and subsequently introducing an alkaline liquor.

6. The improvement in the cooking of wood for the production of wood pulp therefrom which comprises subjecting wood chips in a digester to the action of sulfurous acid and subsequently introducing an alkaline liquor, the amount of alkaline liquor introduced being sufiicient to give an alkaline cooking liquor.

7. The improvement in the sulfite process which comprises subjecting the charge in the digester to a preliminary digestion with an acid sulfite liquor, and subsequently introducing an alkaline liquor and subjecting the charge to a further digestion.

8. The improvement in the sulfite process which comprises subjecting the charge in the digester to a preliminary digestion with an acid sulfite liquor, subsequently introducing an alkaline liquor to give an alkaline cooking liquor and subjecting the charge to a further digestion therewith.

9. The improvement in the cooking of wood which comprises charging wood chips into a digester, removing gases from the digester, thereafter introducing gaseous sulfur dioxide into the digester and subsequently introducing into the digester an alkaline compound in an amount sufficient to convert the sulfur dioxide into a sulfite of an alkali and continuing the cooking of the wood by means of a digestive material comprising the sulfite of an alkali.

10. The process of claim 9 in which the alkaline compound is added in an amount sufiicient to make the digestive material alkaline to litmus.

11. The improvement in the production of pulp which comprises charging wood chips into adigester, removing air from the digester, heating a liquor to remove sulfur dioxide. introducing such sulfur dioxide into the digester under conditions such that wood chips absorb the free sulfur dioxide, partially cooking the wood chips with aqueous material containing a water soluble sulfite, introducing into the digester a compound of alkali in an amount sufficient to neutralize all of the free sulfurous acid and continuing the cooking operation until the fibers are rendered readily separable from each other.

12. The improvement in the production of wood pulp which comprises subjecting wood chips in a digester to the action of sulfurous acid subsequently introducing an alkaline compound in the presence of an aqueous material, the amount of the compound introduced being suflicient to give an alkaline liquor, and subsequently treating the cellulosic fibrous material with such. alkallne liquor containing an alkali metal sulfite so as to remove some of the organic matter then present with the fibres.

13. A process of producing wood pulp having a high percentage of resistant cellulose, which comprises first digesting wood 1n an acid sulphite liquor under heat and pressure, adding to the mass of wood and acid liquor sufficient alkali to render the liquor alkaline,

I and further digesting the wood in such alkaline liquor.

14. A process of producing wood pulp having a high percentage of resistant cellulose, which comprises first digesting wood in a sulphurous acid solution containing sodium sulphite under heat and pressure, adding to the mass of wood and acid liquor suflicient alkaline sodium compounds to render the liquor alkaline, and further digesting the wood under pressure in such alkaline liquor.

15. A process of producing wood pulp having a high percentage of resistant cellulose, which comprises first digesting wood in an acid sulphite liquor under heat and pressure in a closed digester, adding to the mass of wood and acid liquor in the digester sufiicient alkali to render the liquor alkaline, continuing the digestion in said digester, and separating and washing the resultant pulp.

16. A process which comprises first digesting wood in an acid sulphite solution under heat and pressure, adding to the mass of wood and acid liquor in the digester suiiicient alkali to render the liquor alkaline, continuing the digestion in said digester, separating and washing the resultant pulp from the spent liquor of digestion, and recovering the inorganic compounds from the spent liquor.

17. A process which comprises first digesting wood in an acid sodium sulphite solution under heat and pressure, adding to the mass of wood and acid liquid in the digester suflicient caustic soda to render the liquor distinctly alkaline, continuing the digestion in said digester, separating the pulp and the spent liquor of digestion, and recovering the sodium compounds from the liquor.

18. The improvement in the cooking of wood for the production of pulp therefrom which comprises charging the wood chips into a digester, removing air from the digester, introducing sulfur dioxide into the digester, subjecting the chips to a preliminary treatment with the absorbed sulfur dioxide, thereafter introducing into the digester a com pound of an alkali in the presence of aqueous material and continuing the cooking operation with the aqueous material which con tains a sulfite of an alkali, the compound of an alkali being introduced in an amount sufficient to provide a sulfite of an alkali within the wood chips and to substantiall neutralize the acid formed by absorption 0 the sulfur dioxide.

19. The process of treating wood which comprises the following steps: (a) subjecting wood to a digesting treatment by means of a sulfite in aqueous solution so as to solubilize some of the non-cellulosic organic matter thereof; (b) subsequently treating the cellulose-containing material, by means of liquor of different composition containing added alkaline constituents and which contains a re ducing sulfur-bearing compound of an alkali and which is maintained alkaline, so as to obtain at the termination of such treatment an alkaline residual liquor containing dissolved matter derived in part from non-cellulosic organic matter; and (a) subsequently separating the cellulosic fibres from the alkaline residual liquor.

20. The process of treating fibre-bearing material, which comprises the following steps: (a) subjecting wood to a digesting treatment by means of a sulfite in an acid aqueous solution so as to solubilize a part but not all of the non-cellulosic organic matter thereof; (b) subsequently treating the fibre bearing material with an alkaline liquor containing' a non-oxidizing sulfur-containing alkaline reagent, which is capable of solubilizing a portion of the organic ingredients thereof and which is maintained alkaline, so as to obtain at the termination of such treatment an alkaline residual liquor containing dissolved matter derived in part from such organic ingredients; and (c) subsequently separating the cellulosic fibres from the alkaline residual liquor.

21. The process of treating fibre-bearing material, which comprises the following steps: (a) subjecting wood to a digesting treatment by means of a sulfite in aqueous solution so as to obtain a residual liquor which contains dissolved organic matter and also contains a dissolved sulfite; b) subsequently supplying to the resulting fibre-bearing ma terial an alkaline reagent which is capable of solubilizing a portion of the organic ingredients thereof, and treating the fibre-bearing material by means of liquor that contains a sulfite and is maintained alkaline, so as to ob tain at the termination of such treatment an alkaline residual liquor containing dissolved matter derived in part from such organic ingredients; and (c) subsequently separating the cellulosic fibres from the alkaline residual liquor.

22. The process of treating fibre-bearing material, which comprises the following steps: (a) subjecting wood to a digesting treatment by means of a sulfite in aqueous solution so as to solubilize some of the non-cellulosic organic matter thereof and so as to obtain a residual liquor which contains dissolved organic matter and also contains'the sulfite radicle; (b) subsequently supplying an alkaline reagent to the resulting fibrebearing material in the presence of such a residual liquor, the alkaline reagent being added in sufiicient amount to neutralize any free acid contained in the liquor then present with the fibre-bearing material and to leave some of such alkaline reagent in the resulting 1o liquor; (0)- treating the fibre-bearing material, by means of liquor that contains a sulfite and is maintained alkaline, so as to obtain at the termination of such treatment an alkaline residual liquor that contains dissolved 15 matter derived in part from such fibre-bearing material; and (d) subsequently separating the cellulosl: fibres from the alkaline residual liquor.

In testimony whereof we affix our signa- 2 tures.

LINN BRADLEY. EDWARD P. MOEEFE. 

